Much effort has been expended over the last several decades to modify the surface chemistry of carbon black. While it is possible to deposit physically adsorbed material onto the surface of carbon black, permanently changing the surface chemistry of carbon black is substantially more difficult.
Some processes for chemically changing the surface of carbon black are known and used commercially. For example, it is well known that a carbon black surface can be oxidized with a variety of treating agents. Surface oxidation is used to make some commercial products. Sulfonation using sulfuric acid or chlorosulfuric acid and halogenation of a carbon black surface are also known. Some known methods for grafting polymers to the carbon black surface are reviewed by Tsubakowa in Polym. Sci., Vol. 17, pp 417-470, 1992. See also U.S. Pat. No. 4,014,844 which grafts polymers onto carbon black by contacting the carbon black with the polymer and heating.
U.S. Pat. No. 3,479,300 describes carbon catalyst compositions and a process for their production. The catalyst compositions are prepared by treating carbon particles with an alkali or alkaline earth metal and subsequently treating the resulting carbon/metal composition with a solvating ether. The carbon portions of the catalytic compositions can be reacted with various reagents, including organic compounds, to produce carbon compositions.
U.S. Pat. No. 3,043,708 describes modified carbon blacks having hydrocarbon groups chemically attached to the surface of the carbon black. The modified carbon blacks are prepared by reacting carbon black with an alkylating agent in the presence of a Friedel-Crafts type reaction catalyst. The hydrocarbon groups which reportedly can attach to the surface of the carbon black include aliphatic and aromatic groups. A modified carbon black containing aryl groups attached to the surface of a carbon black is reported as being preparable by reacting a halogenated carbon black with an aromatic hydrocarbon in the presence of a Friedel-Crafts type catalyst. U.S. Pat. No. 3,025,259 describes rubber compositions containing the modified carbon blacks of U.S. Pat. No. 3,043,708.
U.S. Pat. No. 3,335,020 describes modified carbon blacks where the carbon black is treated with benzene which is then polymerized on the carbon black. To prepare these modified carbon blacks, benzene and carbon black are mixed with a Lewis Acid catalyst under anhydrous conditions for about ten minutes. The benzene on the carbon black is then polymerized to parapolyphenyl by means of a combination co-catalyst-oxidizing agent and is reportedly thereby bonded to the carbon black.
U.S. Pat. No. Nos. 2,502,254 and 2,514,236 describe the manufacture of pigments containing carbon black. U.S. Pat. No. 2,502,254 reports that highly dispersed pigments suitable for mass pigmentation of viscose can be obtained by generating an azo pigment in the presence of carbon black.
The pigment is produced by coupling a diazotized amine and another usual intermediate for a yellow, orange, or red pigment in the presence of carbon black in one or the other of the aqueous solutions of which the mixing brings about the coupling. U.S. Pat. No. 2,514,236 reports that this process can also prepare a chocolate brown pigment by coupling one molecular proportion of a tetrazotized benzidine with two molecular proportions of an arylmethyl pyrazolone in the presence of carbon black.
PCT Patent Application No. WO 92/13983 describes a process for modifying the surfaces of carbon-containing materials by electrochemical reduction of diazonium salts. The process is reportedly applicable, in particular, to carbon plates and carbon fibers for composite materials. Carbon-containing materials modified by the process are also described. Electrochemical reduction of diazonium salts containing functionalized aryl radicals to covalently modify carbon surfaces is also described in Delmar et al., J. Am. Chem. Soc. 1992, 114, 5883-5884.
According to WO 92/13983, the process for modifying the surface of a carbon-containing material consists of grafting an aromatic group to the surface of this material by electrochemical reduction of a diazonium salt including this aromatic group. The carbon-containing material is placed in contact with a diazonium salt solution in an aprotic solvent and is negatively charged with respect to an anode which is also in contact with the diazonium salt solution. Use of a protic solvent is reported to prevent the electrochemical process from producing the intended product as a result of reducing the diazonium triple bond to yield a hydrazine.
Despite the technology discussed above, there remains a need to modify the surface chemistry of carbon black and impart desired properties to the carbon black.